Showing papers on "Catalyst support published in 2009"

Carbon supports for low-temperature fuel cell catalysts

Abstract: To increase their electrochemically active surface area, catalysts supported on high surface area materials, commonly carbons, are widely used in low-temperature fuel cells. Recent studies have revealed that the physical properties of the carbon support can greatly affect the electrochemical properties of the fuel cell catalyst. It has been reported that carbon materials with both high surface area and good crystallinity can not only provide a high dispersion of Pt nanoparticles, but also facilitate electron transfer, resulting in better device performance. On this basis, novel non-conventional carbon materials have attracted much interest as electrocatalyst support because of their good electrical and mechanical properties and their versatility in pore size and pore distribution tailoring. These materials present a different morphology than carbon blacks both at the nanoscopic level in terms of their pore texture (for example mesopore carbon) and at the macroscopic level in terms of their form (for example microsphere). The examples are supports produced from ordered mesoporous carbons, carbon aerogels, carbon nanotubes, carbon nanohorns, carbon nanocoils and carbon nanofibers. The challenge is to develop carbon supports with high surface area, good electrical conductivity, suitable porosity to allow good reactant flux, and high stability in fuel cell environment, utilizing synthesis methods simple and not too expensive. This paper presents an overview of carbon supports for Pt-based catalysts, with particular attention on new carbon materials. The effect of substrate characteristics on catalyst properties, as electrocatalytic activity and stability in fuel cell environment, is discussed.

Water Gas Shift Catalysis

Abstract: Developments in water gas shift (WGS) catalysis, especially during the last decade, are reviewed. Recent developments include the development of 1 chromium‐free catalysts that can operate at lower steam to gas ratios and 2 more active catalysts that can operate at gas hourly space velocities above 40,000 h−1. A current challenge is to develop catalysts for use in fuel cell applications. Precious metal catalysts supported on partially reducible oxide supports (Pt‐ceria, Pt‐titania, Au‐ceria, etc.) are the current front runners. A critical review of the mechanism of the WGS reaction is also presented.

Coordinatively Unsaturated Al3+ Centers as Binding Sites for Active Catalyst Phases of Platinum on γ-Al2O3

Abstract: In many heterogeneous catalysts, the interaction of metal particles with their oxide support can alter the electronic properties of the metal and can play a critical role in determining particle morphology and maintaining dispersion. We used a combination of ultrahigh magnetic field, solid-state magic-angle spinning nuclear magnetic resonance spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy coupled with density functional theory calculations to reveal the nature of anchoring sites of a catalytically active phase of platinum on the surface of a γ-Al 2 O 3 catalyst support material. The results obtained show that coordinatively unsaturated pentacoordinate Al 3+ (Al 3+ penta ) centers present on the (100) facets of the γ-Al 2 O 3 surface are anchoring Pt. At low loadings, the active catalytic phase is atomically dispersed on the support surface (Pt/Al 3+ penta = 1), whereas two-dimensional Pt rafts form at higher coverages.

Novel catalyst support materials for PEM fuel cells : current status and future prospects

Abstract: Catalyst support materials exhibit great influence on the cost, performance, and durability of polymer electrolyte membrane (PEM) fuel cells. This feature article summarizes several important kinds of novel support materials for PEM fuel cells (including direct methanol fuel cells): nanostructured carbon materials (carbon nanotubes, carbon nanofibers, mesoporous carbon), conductive doped diamonds and nanodiamonds, conductive oxides (tin oxide/indium tin oxide, titanium oxide, tungsten oxide), and carbides (tungsten carbides). The advantages and disadvantages, the acting mechanism to promote electrocatalytic performance, and the strategies to improve present catalyst support materials and search for new ones are discussed. This is expected to shed light on future development of catalyst supports for PEM fuel cells.

Selective phenol hydrogenation to cyclohexanone over a dual supported Pd-Lewis acid catalyst.

Abstract: Cyclohexanone is an industrially important intermediate in the synthesis of materials such as nylon, but preparing it efficiently through direct hydrogenation of phenol is hindered by over-reduction to cyclohexanol Here we report that a previously unappreciated combination of two common commercial catalysts-nanoparticulate palladium (supported on carbon, alumina, or NaY zeolite) and a Lewis acid such as AlCl3-synergistically promotes this reaction Conversion exceeding 999% was achieved with >999% selectivity within 7 hours at 10-megapascal hydrogen pressure and 50 degrees C The reaction was accelerated at higher temperature or in a compressed CO(2) solvent medium Preliminary kinetic and spectroscopic studies suggest that the Lewis acid sequentially enhances the hydrogenation of phenol to cyclohexanone and then inhibits further hydrogenation of the ketone

A Self-Healing Oxygen-Evolving Catalyst

Abstract: A cobalt−phosphate water-oxidizing catalyst forms from the oxidation of Co2+ to Co3+ in the presence of phosphate. We have employed radioactive 57Co and 32P isotopes to probe the dynamics of this catalyst during water-oxidation catalysis. We show that the catalyst is self-healing and that phosphate is the crucial factor responsible for repair.

Carbon materials for catalysis

Abstract: 1 Physico-chemical properties of carbon materials: a brief overview (Ljubisa R. Radovic) . 1.1 Introduction. 1.2 Formation of Carbons. 1.3 Structure and Properties of Carbons. 1.4 Reactions of Carbons. 1.5 Summary and Conclusions. 1.6 References. 2. Surface chemistry of carbon materials (Teresa J. Bandosz) . 2.1 Introduction . 2.2 Surface functionalities. 2.3 Surface modifications. 2.4 Characterization of surface chemistry. 2.5 Role of surface chemistry in the reactive adsorption on activated carbons. 2.6 Role of carbon surface chemistry in catalysis. 2.7 References. 3. Molecular Simulations applied to adsorption on and reaction with carbon (Zhonghua (John) Zhu). 3.1 Introduction. 3.2 Molecular simulation methods applied to carbon reactions. 3.3 Hydrogen adsorption on and reaction with carbon. 3.4 Carbon reactions with oxygen containing gases. 3.5 Metal-Carbon interactions. 3.6 Conclusions. 3.7 References. 4. Carbon as catalyst support (Francisco Rodr!guez-Reinoso and Antonio Sepulveda-Escribano). 4.1 Introduction. 4.2 Carbon properties affecting its role as catalyst support. 4.3 Preparation of carbon supported catalysts. 4.4 Applications. 4.5 Summary. 4.6 References. 5. Preparation of carbon-supported metal catalysts (Johannes H. Bitter and Krijn P. de Jong). 5.1 Introduction. 5.2 Impregnation/adsorption. 5.3 Deposition Precipitation. 5.4 Emerging preparation methods. 5.5 Concluding remarks. 5.6 References. 6. Carbon as catalyst (Jos' Luis Figueiredo and Manuel Fernando R. Pereira). 6.1 Introduction. 6.2 Factors affecting the performance of a carbon catalyst. 6.3 Reactions catalyzed by carbons. 6.4 Conclusions. 6.5 References. 7. Catalytic properties of nitrogen-containing carbons (Hanns-Peter Boehm). 7.1 Introduction. 7.2 Nitrogen-doping of carbons. 7.3 Catalysis of oxidation reactions with dioxygen. 7.4 Catalysis of aging of carbons. 7.5 Catalysis of dehydrochlorination reactions. 7.6 Conclusions on the mechanism of catalysis by nitrogen-containing carbons. 7.7 References. 8. Carbon anchored metal complex catalysts (Cristina Freire and Ana Rosa Silva). 8.1 Introduction. 8.2 General methods for molecule immobilization. 8.3 Methods for immobilization of transition metal complexes onto carbon materials . 8.4 Application of coordination compounds anchored onto carbon material in several catalytic reactions . 8.5 Carbon supported organometallic compounds in hydrogenation and hydroformylation catalytic reactions . 8.6 Carbon supported organometallic complexes in polymerisation reaction of olefins. 8.7 Concluding Remarks. 8.8 References. 9. Carbon nanotubes and nanofibers in catalysis (Philippe Serp). 9.1 Introduction. 9.2 Catalytic growth of carbon nanofibers and carbon nanotubes. 9.3 Why can CNTs or CNFs be suitable to be used in catalysis?. 9.4 Preparation of supported catalysts on CNTs and CNFs. 9.5 Catalytic performance of CNT- and CNF-based catalysts. 9.6 Conclusion. 9.7 References. 10. Carbon gels in catalysis (Carlos Moreno-Castilla). 10.1 Introduction. 10.2 Carbon gels: preparation and surface properties. 10.3 Metal-doped carbon gels. 10.4 Catalytic reactions of metal-doped carbon gels. 10.5. Conclusions. 10.6 References. 11. Carbon monoliths in catalysis (Karen M. de Lathouder, Edwin Crezee, Freek Kapteijn and Jacob A. Moulijn). 11.1 Introduction. 11.2 Carbon. 11.3 Monolithic structures. 11.4 Carbon monoliths. 11.5 Carbon monoliths in catalysis: an overview. 11.6 Example of carbon monoliths as catalyst support material. 11.7 Evaluation and Practical Considerations. 11.8 Conclusions. 11.9 References. 12. Carbon materials as supports for fuel cells electrocatalysts (Frederic Maillard, Pavel A. Simonov and Elena R. Savinova). 12.1 Introduction. 12.2 Structure and morphology of carbon materials. 12.3 Physicochemical properties of carbon materials relevant to the fuel cell operation. 12.4 Preparation of carbon-supported electrocatalysts. 12.5 Structural characterization of carbon-supported metal catalysts. 12.6 Influence of carbon supports on the performance of the catalytic layers in PEMFCs. 12.7 Corrosion and stability of carbon-supported catalysts. 12.8 Conclusions and outlook. 12.9 References. 13. Carbon materials in photocatalysis (Joaquim Lu!s Faria and Wendong Wang). 13.1 Introduction. 13.2 Different carbon materials employed to modify TiO2 in photocatalysis. 13.3. Synthesis and characterization of carbon-TiO2 composites. 13.4 Photodegradation on carbon containing surfaces. 13.5. Role of the carbon phase in heterogeneous photocatalysis. 13.6. Concluding remarks. 13.7 References. 14. Carbon-based sensors (Jun Li). 14.1 Introduction. 14.2 The physico-chemical properties of sp2 carbon materials relevant to carbon sensors. 14.3 Carbon-based sensors. 14.4 Summary. 14.5 References. 15. Carbon Supported Catalysts for the Chemical Industry (Venu Arunajatesan, Baoshu Chen, Konrad Mobus, Daniel J. Ostgard, Thomas Tacke and Dorit Wolf). 15.1 Introduction. 15.2 Properties and Requirements of Carbon Materials as Catalyst Supports for Industrial Applications. 15.3 Industrial manufacturing of carbon supports. 15.4 Manufacturing of Carbon Supported Catalysts. 15.5 Reaction Technology. 15.5.1 Batch stirred-tank and loop reactors. 15.6 Industrial Applications. 15.7 Testing and Evaluation of Carbon Catalysts. 15.8 Conclusions and Outlook. 15.9 References.

Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity

Abstract: The present disclosure is directed to a method of producing metallic single-wall carbon nanotubes by treatment of carbon nanotube producing catalysts to obtain the desired catalyst particle size to produce predominantly metallic single wall carbon nanotubes. The treatment of the carbon nanotube producing catalyst particles involves contacting the catalyst particles with a mixture of an inert gas, like He, a reductant, such as H 2 , and an adsorbate, like water, at an elevated temperature range, for example, at 500° C. to 860° C., for a sufficient time to obtain the catalyst particle size. In some of the present methods, the preferential growth of nanotubes with metallic conductivity of up to 91% has been demonstrated.

Nanoplasmonic Probes of Catalytic Reactions

Abstract: Optical probes of heterogeneous catalytic reactions can be valuable tools for optimization and process control because they can operate under realistic conditions, but often probes lack sensitivity. We have developed a plasmonic sensing method for such reactions based on arrays of nanofabricated gold disks, covered by a thin (~10 nanometer) coating (catalyst support) on which the catalyst nanoparticles are deposited. The sensing particles monitor changes in surface coverage of reactants during catalytic reaction through peak shifts in the optical extinction spectrum. Sensitivities to below 10−3 monolayers are estimated. The capacity of the method is demonstrated for three catalytic reactions, CO and H2 oxidation on Pt, and NOx conversion to N2 on Pt/BaO.

Synthesis of Solid Catalysts

Abstract: PART I: Basic Principles and Tools GENERAL ASPECTS Importance of Solid Catalysts Development of Solid Catalysts Development of Solid Catalyst Synthesis About this book INTERFACIAL CHEMISTRY Introduction Interfacial and Bulk Deposition The Surface of the Oxidic Supports: Surface Ionization Models The Size and the Structure of the Interface The Arrangement of the Ions Inside the Interface and the Deposition Modes Determining the Mode of Interfacial Depostion and the Surface Speciation/Structure of the Deposited Precursor Species A Case Study: The Deposition of Co(H2=)6 2+ Aqua Complex on the Titania Surface ELECTROSTATIC ADSORPTION Introduction Purely Electrostatic Adsorption Electrostatic Adsorption with Metal Respeciation Electrostatic Adsorption and Ion Exchange Electrostatic Adsorption and Deposition-Precipitation Electrostatic Adsorption and Surface Reaction Electrostatics and Dissolution, Reaction, and Redeposition Electrostatics-Based Design IMPREGNATION AND DRYING Introduction Impregnation Drying The Chemistry Impregnation and Drying of an MoOx/Al2O3 Catalyst SOL-GEL PROCESSING Introduction Physicochemical Basis and Principles of Sol-Gel Processing Application of Sol-Gel Processing for the Preparation of Solid Catalysts DEPOSITION PRECIPITATION Introduction Theory and Practice Mechanistic Studies Case Studies COPRECIPITATION Introduction Basic Principles of Precipitation and Nucleation Raw Materials Precipitation Conditions Process Operation Examples New Developments in Process Monitoring CLUSTERS AND IMMOBILIZATION Introduction The Surface of Common Supports Clusters in Catalysis Reaction with Unmodified Surface "Ship-in-a-Bottle" Synthesis Tethering SHAPING OF SOLID CATALYSTS Objectives of Catalyst Shaping Fixed-Bed Reactors - Particle Beds Fixed-Bed Reactors - Monoliths Catalysts for Moving-Bed Reactors Catalysts for Fluidized Beds SPACE AND TIME-RESOLVED SPECTROSCOPY OF CATALYST BODIES Introduction Space- and Time-Resolved Methods Applied to Catalyst Bodies Case Studies Future Prospects HIGH-THROUGHPUT EXPERIMENTATION Introduction Synthesis Strategies Catalyst Libraries for Primary Screening Catalyst Libraries for Secondary Screening Catalyst Libraries for Special Reactor Types An Industrial Point of View PART II: Case Studies CONCEPTS FOR PREPARATION OF ZEOLITE-BASED CATALYSTS Introduction and Scope Zeolite Effects in Catalysis Zeolitization ORDERED MESOPOROUS MATERIALS Introduction Mesoporous Silica Organic Group Functionalized Mesoporous Silicates Metal-Substituted Mesoporous Silica Molecular Sieves Carbon Nonsiliceous Oxides Nonoxides HYDROTREATING CATALYSTS Introduction Typical Hydrotreating Catalyst Support Preparation Metal Comixing/Coextrusion and Coprecipitation Routes Impregnation of Metals Presulfiding as the Last Stage in Hydrotreating Catalyst Preparation Industrial Process for the Production of the Oxidic Catalyst METHANOL CATALYSTS Binary Cu/ZnO Catalysts Coprecipitation The Role of Alumina in Ternary Catalysts Alternative Preparation Routes CASE STUDIES OF NOBEL-METAL CATALYSTS Introduction Optimization of Catalyst Preparation GOLD CATALYSTS Introduction Preparations Involving Aqueous Solutions Preparations Involving Organometallic Precursors Deposition of Gold Nanoparticles One-Step Preparations Special Methods

Carbon nanotube-supported Pd-ZnO catalyst for hydrogenation of CO2 to methanol

Abstract: National Natural Science Foundation [20590364]; National Basic Research ("973") Project of China [2005CB221403]

Hydrogen production by steam gasification of polypropylene with various nickel catalysts

Abstract: Several nickel-based catalysts (Ni/Al2O3, Ni/MgO, Ni/CeO2, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO2/Al2O3) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500 °C and gasification temperature was kept constant at 800 °C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al2O3 was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2 wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7 wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H2 production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H2 production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3 wt.% of theoretical) from the pyrolysis–gasification of polypropylene.

Selective methanation of CO over supported Ru catalysts

Abstract: The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO 2 has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al 2 O 3 , TiO 2 , YSZ, CeO 2 and SiO 2 ). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H 2 15% CO 2 and 0–30% H 2 O (balance He). It has been found that, for all catalysts investigated, conversion of CO 2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO 2 methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO 2 hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO 2 catalysts, TOFs of both CO (at 215 °C) and CO 2 (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al 2 O 3 . Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO 2 , compared to YSZ or SiO 2 , whereas CeO 2 - and Al 2 O 3 -supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO 2 catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO 2 conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO 2 catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.

Deoxygenation of palmitic and stearic acid over supported Pd catalysts: Effect of metal dispersion

Abstract: Catalytic deoxygenation of palmitic and stearic acids mixture was studied over four synthesized Pd catalysts supported on synthetic carbon (Sibunit) in a semibatch reactor and dodecane as a solvent at 260–300 °C. The catalysts were prepared by precipitation deposition method using Pd chlorides as metal precursors. All catalysts contained 1 wt.% Pd, however, the metal dispersion was systematically varied. An optimum metal dispersion giving the highest reaction rate was observed. The main liquid phase products were n-heptadecane and n-pentadecane, which were formed in parallel. In addition to the particle size effect the impact of mass transfer was elucidated and a detail discussion on temperature programmed desorption of CO from the fresh and spent samples was provided.

The effect of CeO2 on the surface and catalytic properties of Pt/CeO2–ZrO2 catalysts for methane dry reforming

Abstract: The CO2 reforming of CH4 over Pt catalysts supported on nanocrystalline mesoporous ZrO2 and CeO2–ZrO2 carriers was investigated at atmospheric pressure. The effect of CeO2 content (1–12 wt%) on the surface and catalytic properties of the catalysts was studied. It was found that the pre-treatment temperature and the concentration of CeO2 influence on the morphology of Pt particles. The calcination temperature as high as 1073 K leads to sintering of Pt particles deposited over zirconia- and CeO2-loaded zirconia substrates. Temperature-programmed reduction (TPR) results showed good reductive properties for Pt/CeO2–ZrO2 catalysts due to both, the high surface shell reduction of zirconia and the synergetic effect between Pt and CeO2. X-ray photoelectron spectroscopy (XPS) of reduced catalysts revealed the presence of different Pt oxidation state depending on the catalyst composition. Stabilization of partially oxidized platinum species by ceria was detected for the reduced Pt/CeO2–ZrO2 samples. An activation period was required for the stabilization of the activity of Pt/CeO2–ZrO2 catalysts. The high stability of Pt/CeO2–ZrO2 catalysts was related to the close contact between Pt and CeO2.

Carbon deposition as a deactivation mechanism of cobalt-based Fischer-Tropsch synthesis catalysts under realistic conditions

Abstract: Deactivation of cobalt-based Fischer–Tropsch synthesis (FTS) catalysts by carbonaceous species has been previously postulated. This mechanism, however, is difficult to prove due to the presence of long chain hydrocarbon wax product and the potential accumulation of inactive carbon on the catalyst support. Furthermore, due to the slow build-up of low quantities of inactive carbon with time on stream, the investigation of carbon deposition necessitates the use of data from extended FTS runs. In this study, the formation of carbon deposits on samples of a Co/Pt/Al2O3 catalyst, taken from a 100-barrel/day slurry bubble column reactor operated over a period of 6 months at commercially relevant FTS conditions is reported. The spent catalysts were wax extracted in an inert environment and the amount, nature and location of carbon deposits were then studied using temperature programmed hydrogenation and oxidation (TPH/TPO), energy filtered transmission electron microscopy (EFTEM), high sensitivity low energy ion scattering (HS-LEIS) and hydrogen chemisorption. TPH/TPO showed that there is an increase in polymeric carbon with time on stream which may account for a part of the observed long-term catalyst deactivation. Carbon maps from EFTEM as well HS-LEIS data show that the polymeric carbon is located both on the alumina support and cobalt. Although there is clearly an interplay of various deactivation mechanisms which may also include sintering, poisoning and cobalt reconstruction, the evidence presented shows that the polymeric carbon on the metal may be linked with a part of the longer term catalyst deactivation.

Iron catalysts supported on carbon nanotubes for Fischer–Tropsch synthesis: Effect of catalytic site position

Abstract: In order to study the effects of catalytic site position on Fischer–Tropsch (FT) reactions, a method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes (CNTs). TEM analyses revealed that more than 70–80% of iron oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Based on H 2 -TPR analysis, deposition of iron oxide inside the nanotube pores resulted in easier reduction of the oxide at a lower temperature (from 418 to 381 °C). Catalytic performances of the catalysts in terms of FT experiment were tested in a fixed-bed reactor. According to the results of FT experiments, both catalysts showed similar initial %CO conversion (∼90%). However, the catalyst with catalytic sites inside the pores exhibited higher selectivity to heavier hydrocarbons. In addition, deposition of catalytic sites on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced deactivation within a period of 125 h due to catalytic sites sintering. It is concluded that encapsulation of catalytic sites inside the nanotubes prevents the catalytic site agglomeration.

State of Transition Metal Catalysts During Carbon Nanotube Growth

Abstract: We study catalyst−support and catalyst−carbon interactions during the chemical vapor deposition of single-walled carbon nanotubes by combining environmental transmission microscopy and in situ, time-resolved X-ray photoelectron spectroscopy. We present direct evidence of what constitutes catalyst functionality by comparing the behavior of Ni, Fe, Pd, and Au model catalyst films on SiO2 during preannealing in O2 and NH3 and during C2H2 decomposition. The catalyst metal surface supplies sites to dissociate the hydrocarbon precursor and then guides the formation of a carbon lattice and the liftoff of a carbon cap. The catalysts are sharply distinguished by their reactivity toward activation of the hydrocarbon precursor, following trends known from heterogeneous catalysis. For Fe and Ni, the active state of the catalyst is a crystalline metallic nanoparticle. Graphitic networks do not form on oxidized Fe. Pd forms a silicide on SiO2 under our reducing conditions. Pd (silicides) and Au nanocrystals are catalyt...

Tunable catalyst gas phase hydrogenation of carboxylic acids

Abstract: A process for selective formation of ethanol from acetic acid includes contacting a feed stream containing acetic acid and hydrogen at an elevated temperature with catalyst comprising platinum and tin on a high surface area silica promoted with calcium metasilicate Selectivities to ethanol of over 85% are achieved at 280° C with catalyst life in the hundreds of hours